This invention pertains to apparatus for making sheet-like elastomers mixed with short fibers.
Japanese Unexamined Patent Application No. 4-80013 discloses a device for making short-fiber-containing elastomers (FIG. 3). This apparatus has an expanding die 1 formed by an external die 1A and an internal die 1B together defining an annular area, and an enlarging adapter 3. The apparatus further includes a screw pin 4 which connects the external die 1A and the internal die 1B, a washer 6, and a nut 5.
The expanding die 1A extrudes an elastomeric material E mixed with short fibers into a tubular form wherein the short fibers are oriented in the circumferential direction. The enlarging adapter 3 circumferentially enlarges the elastomer thus extruded. As a result, a tubular elastomer Ep with high circumferential orientation is made and converted into a sheet-like elastomer Es. Such conversion is described. A cutter 10a is provided at an outlet end of the enlarging adapter 3. The cutter 10a continuously slits the oncoming tubular elastomer Ep in the axial direction. A development unit 20a spreads out the tubular elastomer Ep with a longitudinal slit through it thereby forming a sheet-like elastomer Es. This development unit 20a is formed by arranging many conveyers in such a way that they are tangent to a semicircle at their leading ends while they are tangent to a plane at their trailing ends.
The above-described technique, however, presents several drawbacks. The orientation of each short fiber F is in disorder (i.e. out of anti-grain orientation). As seen from FIG. 4, the orientation of each short fiber F is advanced at the middle region of the sheet-like elastomer Es while on the other hand the orientation is delayed at each lateral edge region. The orientation of each short fiber F results in arcing. Taking d=the maximum width of the short fiber's F are and W=the width of the sheet-like elastomer Es, d/W is about 0.07 to 0.15. When such a sheet-like elastomer Es is cut later, this will give rise to the flare of each lateral edge region as shown in FIG. 5.
The above presents another problem. For example, when making tubular belts from the prior art sheet-like elastomer, its base rubbers results in having different lengths. For this reason, it is not advantageous to manufacture tubular belts with such a conventional material. Particularly, it is impossible to get the leading and trailing ends of a sheet-like elastomer butted against each other. Butt Joints are not available.
Even if the aforesaid difficulties are overcome by increasing the number of manufacturing steps, this will present another difficulty. That is, when spinning a post-vulcanization tubular belt hung over a roll-like jig for engraving, the tubular belt will not be secured over the roll-like jig because the orientation of fibers in a base rubber is in disorder, resulting in moving backwards or forwards over the roll-like jig. For this reason, it is hard to form a V-shaped belt. To cope with this problem, it will become necessary to secure a tubular belt to a roll-like. jig. This means that the processing becomes complicated.
Additionally, since the orientation of short fibers is in disorder, this seriously affects the quality of elastomer products.
The reason for these problems has been investigated and the following come to be known. For the case of extrusion by means of so-called anti-grain orientation in which short fibers are oriented circumferentially, the pressure of rubber at the time of extrusion, which varies depending upon the Mooney viscosity of the rubber, the temperature of the rubber, the thickness of a desired sheet-like elastomer, the velocity of extrusion, usually reaches 300 kg/cm.sup.2. The temperature at a die outlet end goes beyond 100.degree. C. Such a pressured rubber (i.e. 300 kg/cm.sup.2) is released all at once into atmospheric air and at the same time the contained short fibers are oriented circumferentially. Under such situation, the sheet-like elastomer is cut by means of a cutter, as a result of which sudden stress relaxation will occur. Such stress relaxation occurs pronouncedly at a particular point (i.e. at a point at which a sheet-like elastomer is cut at a later manufacturing step), which causes serious shrinkage in the circumferential direction as well as in the extrusion direction. Meanwhile, the degree of stress relaxation then is low at a point on the circumference (i.e. at the middle of the sheet-like elastomer) opposite the cut point. Such a cut tubular elastomer whose temperature is about 100.degree. C. is pulled out by the development unit 20a in order to avoid heat-distortion, thereafter being cooled and developed into a flat form. However, due to the above-described difference in the degree of stress relaxation, the orientation of short fibers is advanced at the middle and while it is delayed at the lateral edge, as described previously with reference to FIG. 4.
Furthermore, when a tubular elastomer is cut and developed into a flat form (see FIG. 6), a distance L2 (i.e. a distance from a cut point to one lateral edge region point at which the tubular elastomer becomes flat) and a distance L3 (i.e. a distance from the cut point to the other lateral edge region point at which the tubular elastomer becomes flat) are longer than a distance L1 from a point on the circumference of the tubular elastomer opposite the cut point to the middle end point at which the tubular elastomer becomes flat. These three different distances L1, L2, and L3 become equal only when they are infinite. Practically, the distance restrictions occur, and the difference in length is inevitable.
The present invention is made in an effort to overcome the above-mentioned problems in the prior art techniques. It is a general object of the present invention to provide an improved apparatus in which, while keeping a tubular elastomer extruded from an outlet in a tubular form, uniform stress relaxation grows in the circumferential direction. At the time when such stress relaxation disappears, the tubular elastomer is subjected to the process of cutting. Optionally, in a process during which a tubular elastomer becomes a sheet-like elastomer, the difference in length described above is canceled. In this way, the orientation of short fibers contained in a sheet-like elastomer is unified.